A lot depends on the market, US made ones aimed for this country stayed Imperial [inch] until production ended. Ones made in metric countries for sale to the Imperial users usually had Imperial lead screws with the needed gears to cut metric. My '80s Chinese 18" cuts both on the gearbox no loose gears needed,but that is a machine aimed at the commercial market. But at the moment my metric needs are satisfied with taps and dies.

The Clausing doesn't do metric because it's ancient. When it was manufactured, people in places like South Bend were calling metric a fad and saying it would never last. They would lean back on their non-metric lathes and giggle at the ridiculous new Japanese cars that whizzed by their factory.

South Bend Lathe was making lathes that were all metric for years before they closed
their doors. I've seen them. There wasn't much of a market here but in Europe, they
sold better. If you had their parts manual, you can see the part numbers for the metric
lead screw and cross feed screw. So, your comment about South Bend isn't accurate.

John, there was a metric transposing set-up for the 5900 series. I've
got most of one myself. It used the 127/100 transposing gears as well
as a different "banjo" yoke assembly. It is the No. 7124 Metric Thread
Cutting Attachment. There is a 2 page PDF file of the part and installation
instructions over on the Yahoo Clausing Lathe and Mill site in the Files section.

There was a member over there that was selling a newly made kit based
on it for interested people. It was a while back but if your do a search
and send him an email, he might still have a kit left. The difference between
his kit and the Clausing was his "banjo" yoke was make from CNC cutout steel
instead of a casting.

That is because it was a joke. But if we're going to be serious, the serious answer to the OP's question is this: the Clausing doesn't do metric threads without expensive accessories (which are nearly impossible to find) because it's an old American lathe made for American buyers. The current Clausing gearheads have 39 metric pitches straight from the factory, which is probably in China.

Good luck finding those metric threading parts. I found an INCOMPLETE used set for $400 back when I was in Clausing denial. Closest I ever came. The people who told me to get taps and dies were probably right. For less than $400, you can probably do all of your metric threading with taps and dies for the first five years you own the lathe.

People did giggle at Japanese cars. That part is true. Then the Japanese handed Detroit its own backside, in individually wrapped slices. But I digress.

Nitpicking jokes? It will be a great improvement to the forum, and I'm sure everyone is eager to see more of it. It's still expensive to tool a Clausing for metric, and it will take John a long time to change all that crap every time he wants to make a thread. And Plaza Machinery still cheated me, if that's what you're actually thinking about.

FYI, the gentleman that was making the kits for 4900's and 5900's
was selling them for $360 plus $13.45 S+H.

That's all the evidence John needs that he should go with taps and dies or just forget about using the Clausing for metric. If he had paid nothing for the lathe, maybe this large expense could be rationalized, but he paid $100, and he will still have to spend fifteen minutes taking the lathe apart and putting it back together every single time he wants to do metric. For a modern lathe, it takes five seconds, but once the limited-feature Clausing is in the shop, it's too late to think about that.

Hang the expense !! You obviously don't know me well !! In 40 odd years of owning lathes I have never cut a metric thread but, that does not stop me from wanting the needed tooling to do so ! By the way I have taps&dies to 24MM on the shelf.

John Evans wrote:Hang the expense !! You obviously don't know me well !! In 40 odd years of owning lathes I have never cut a metric thread but, that does not stop me from wanting the needed tooling to do so ! .

I had some of the same issues with my old Rockwell 11" lathe, which I still miss from time to time. But a metric threading setup for it was equally difficult to find/build/configure. I really never had issue with it, but nevertheless, native metric support was tentatively on the "must have" portion of my list of features for my subsequent lathe. By that I mean I really wanted it, but if I found an otherwise perfect lathe for a smoking deal that didn't have that feature, I would have been ok dropping the metric threading requirement.

After I got the new lathe (with metric), the very first nontrivial job (standoffs and such) I did on it required a 30mm x 1.5(?) left hand thread to mount a Hayden electric fan clutch (common on medium duty trucks) on a Cummins 6BT transplanted into a 72 Suburban that I helped a friend complete. He really wanted to use that Hayden (new in box smoking deal), but all standard adapters put the fan in the middle of his radiator. So I made an adapter hub. Without metric single point threading, that was a non-starter, and there were NO other sane options except switching to a Dodge viscus.

It sounds like a great piece of metric work combined with the knowledge to correctly apply it. Also, perfect timing.
I have a question about the Delta Rockwell 11" lathe in that thread. Golly, you know about these a long time.